This invention relates, in general, to an improvement in an internal combustion engine, and more particularly to an intake vacuum control device for controlling intake vacuum of the engine within a desirable range.
During deceleration of an engine, a throttle valve disposed in an intake passageway is fully closed even though engine speed is high, and accordingly intake vacuum downstream of the throttle valve is excessively increased. As a result, engine oil is sucked into the combustion chambers of the engine by the action of the increased intake vacuum. This unavoidably increases the oil amount consumed or burnt in the combustion chambers. Additionally, the combustion in the combustion chambers is then temporarily deteriorated to increase the emission levels of carbon monoxide and hydrocarbons.
In order to overcome the above-stated shortcomings, it has already been proposed that an intake vacuum control valve is installed in a bypass passage connecting the upstream and downstream sides of a throttle valve. With this proposition, an excessive increase in intake vacuum can be suppressed by introducing additional air or air-fuel mixture through the intake vacuum control valve during deceleration of the engine. An example of such a proposition is disclosed in U.S. Pat. No. 3,866,583 which shows therein the intake vacuum control valves of diaphragm operated type, of ball valve type using a ball valve, and of the type in which a valve disc is movably mounted on the throttle valve.
However, such the intake vacuum control valves have encountered the problems in which the diaphragm operated type is poor in durability; and the remaining two types are poor in their response and sealing ability. Hence, it has been impossible to achieve an accurate control of the intake vacuum by using the above-mentioned types of prior art intake vacuum control valves.